Semiconductor lasers are attractive for a wide variety of applications including telecommunications, computing systems, optical recording systems and optical interconnection of integrated circuits. Semiconductor lasers provide compact sources of coherent, monochromatic light which can be modulated at high bit rates to transmit large amounts of information.
Vertical-cavity surface emitting lasers (VCSELs) are particularly promising for applications requiring two dimensional arrays of lasers. As contrasted with edge emitting lasers which emit light parallel to the growth planes of their substrates, VCSELs emit perpendicular to the substrates. A typical VCSEL comprises an active region sandwiched between a pair of distributed Bragg reflector stacks. Upon injection of suitable current through the active region, laser light is emitted transverse to the planes of growth.
One difficulty with conventional VCSELs is their relatively low efficiency. Much of the electrical power passing through the resistive reflector stacks is wasted in generating heat rather than light, and the heat generated degrades the operating characteristics of the device. Accordingly, there is a need for a VCSEL device having reduced electrical resistance and providing enhanced optical output.